The aim of this thesis was to investigate the physical mechanisms that limit the efficiency and reliability of UV-C LED devices supplied by Technische Universität Berlin (TUB), an academic partner of the University of Padua. We studied the mechanisms responsible for the electrical and optical degradation of the device through the application of different advanced analysis techniques. We conducted both electrical and optical characterisations within a thermocontrolled environment to determine the evolution of the devices behaviour when subjected to DC stress. At the same time, we performed Capacitance Deep Level Transient Spectroscopy measurements to determine the traps type, estimate their concentration, identify their activation energy and possibly their energy distribution in a defects band. We then compared the results with literature to find possible correlations to identify their nature. With capacitance measurements, we were able to reconstruct, after some approximations on the space charge region, a charge profile matching the one suggested by the structure, to better recognise the areas on which to focus our analysis and identify the defects spatial distribution. All the work was supported by TCAD simulations, thus enabling a more detailed analysis of both the emission spectrum of the device and its parasitic components, as well as the space charge regions.
Lo scopo di questo lavoro di tesi è stato quello di studiare i meccanismi fisici che limitano l’efficienza e l’affidabilità nei dispositivi LED UV-C forniti dalla Technische Universität Berlin (TUB), partner accademico dell’Università di Padova. I meccanismi responsabili del degrado elettrico ed ottico del dispositivo sono stati ricercati attraverso l’applicazione di numerose tecniche di analisi. Sono state compiute delle caratterizzazioni sia elettriche che ottiche all’interno di un ambiente termocontrollato per determinare l’evoluzione del comportamento del dispositivo sottoposto ad uno stress a corrente continua. Parallelamente sono state eseguite misure di Capacitance Deep Level Transient Spectroscopy al fine di determinare la tipologia delle trappole, stimare la loro concentrazione, identificare la loro energia di attivazione ed eventualmente la loro distribuzione energetica in una banda di difetti. I risultati sono stati poi comparati con la letteratura per trovare possibili correlazioni e cercare di identificare la loro natura. Tramite le misure capacitive, siamo riusciti a ricostruire, dopo alcune approssimazioni dovute all’espansione della regione di carica spaziale, un profilo di carica combaciante con quello della struttura, in modo da poter riconoscere al meglio le zone su cui concentrare le analisi ed individuare la distribuzione spaziale dei difetti. Tutto il lavoro è stato supportato da simulazioni TCAD permettendo così una analisi più dettagliata sia dello spettro di emissione del dispositivo e delle sue componenti parassite , sia delle regioni di carica spaziale.
Investigation of degradation mechanisms and defect analysis in AlGaN-based LEDs in the UV-C range
PILATI, MARCO
2021/2022
Abstract
The aim of this thesis was to investigate the physical mechanisms that limit the efficiency and reliability of UV-C LED devices supplied by Technische Universität Berlin (TUB), an academic partner of the University of Padua. We studied the mechanisms responsible for the electrical and optical degradation of the device through the application of different advanced analysis techniques. We conducted both electrical and optical characterisations within a thermocontrolled environment to determine the evolution of the devices behaviour when subjected to DC stress. At the same time, we performed Capacitance Deep Level Transient Spectroscopy measurements to determine the traps type, estimate their concentration, identify their activation energy and possibly their energy distribution in a defects band. We then compared the results with literature to find possible correlations to identify their nature. With capacitance measurements, we were able to reconstruct, after some approximations on the space charge region, a charge profile matching the one suggested by the structure, to better recognise the areas on which to focus our analysis and identify the defects spatial distribution. All the work was supported by TCAD simulations, thus enabling a more detailed analysis of both the emission spectrum of the device and its parasitic components, as well as the space charge regions.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/33207